How to call C++ code in llvm ... IRBuilder? - c++11

Question

I am using LLVM to build a simple language along the lines demonstrated in the LLVM kaleidoscope documentation. However the doc omits two important things (at least):
how to call C++ code
how to do strings
You can imagine a custom language allows constructs like,
String str("Hello World");
String str1(" and StackOverflow");
str.append(str1);
Since LLVM ships with SmallString, the obvious thing to do is treat the user type String as a llvm::SmallString and emit code for it. But how to do this? I see very little sense in creating a String class from scratch provided there's a way to invoke those C++ calls from LLVM. Would one use IRBuilder to build out the C++ calls?
Another option is to create C++ file containing the equivalent C++ code for the user provided code in terms of llvm::SmallString intermixed with inlined IR code ala the kaleidoscope demo ... and pass the whole thing to Clang/LLVM to compile down to object code. But Clang/LLVM doesn't allow intermixing this way.
Putting aside technicalities of creating static strings that go into the initializer how do people do this? Once this is sorted out for strings, most likely the approach would work for sets, hashmaps, vectors, and all the various other containers LLVM ships with.
LLVM is a strange, cool thing. The things I need are right there, and not readily accessible based on any documentation I can find.
I want a considered approach because even this simple hello world program generates 81 lines of IR code. Replace the llvm::SimpleString with a C-string and the resulting IR code is smaller almost by an order of 10:
#include <llvm/ADT/SmallString.h>
int main(int argc, char **argv)
{
llvm::SmallString<32> str("hello world\n");
printf("%s\n", str.c_str());
return 0;
}
That's a lot of code to hand assemble and we're no where close to supporting all the methods doable for strings.
Thanks.